There are many methods by which to feed an active catalyst composition to gas phase polymerization reactor. These include dry mode addition in which solid catalyst particles are fed directly to a reactor under positive gas pressure (see for example U.S. Pat. Nos. 3,876,602, 5,433,924, 5,240,683, 7,891,527 and references therein), addition of solubilized or unsupported catalyst compositions (see U.S. Pat. Nos. 5,317,036, 5,693,727, 5,948,871 and 6,586,544) and the use of slurry feed systems to deliver suspended catalyst compositions (see for example U.S. Pat. Nos. 4,767,028, 4,610,574, 6,319,995, 6,908,971, 6,936,226, U.S. Pat. Appl. No. 2008/0039596, European Pat. No. 1,660,231 and references therein).
Feeding of traditional Ziegler-Natta and Phillips catalysts, which are solids, in a mineral oil to a gas phase reactor is known to improve catalyst activity (see U.S. Pat. No. 5,362,416) and to reduce fouling associated with static build up (see U.S. Pat. No. 7,202,313) respectively.
Particulate, single site catalysts such as supported metallocenes have been fed to a gas phase reactor as a slurry in inert hydrocarbon liquids including more viscous materials such as mineral oil. Several advantages are claimed to be associated with slurry feeding a supported metallocene catalyst such as improved particle morphology, better control over catalyst feeding rates, improved catalyst pre-polymerization shelf life, improved activity and reduced catalyst feeder and reactor fouling.
European Pat. No. 819,706 B1 demonstrates bulk phase polymerization of propylene using an activated and supported metallocene catalyst fed to a reactor as slurry in mineral oil. An organoaluminum compound is included in the slurry formulation. In U.S. Pat. No. 6,468,936, a similar mineral oil slurry of a supported metallocene catalyst, one which is prepared using a method which involves a solvent removal step, is used to form stereoregular propylene polymers in the slurry phase. The use of the solvent free catalyst in a mineral oil slurry improved post-polymerization reactor clean up. U.S. Pat. Nos. 6,777,366 and 6,777,367 provide another method by which to form a supported catalyst slurry in mineral oil. In this particular method, the catalyst species is combined with a supported activator at temperatures below 10° C. in the presence of solvent, followed by washing with a paraffinic hydrocarbon and dispersal in a mineral oil.
European Pat. Appl. No. 811,638 A2 exemplifies gas phase polymerization in a fluidized bed reactor, in which a supported metallocene slurried in mineral oil (at 20 wt %) is fed to the reactor using a piston-type pump. Isopentane and nitrogen were used to flush the slurry to the reactor. The antistat Atmer-163™ was sprayed into the reactor separately as a dilute solution in isopentane.
U.S. Pat. Appl. No. 2002/0137861 teaches that feeding a slurry of a supported metallocene in Kaydol mineral oil to a gas phase reactor can lead to polymer agglomeration unless the mineral oil slurry further comprises an alkylaluminum scavenger compound. The supported metallocene used in the examples was rac-dimethylsilylbis(tetra-hydroindenyl)zirconium dichloride and the mineral oil slurry contained 20 percent by weight of the supported catalyst.
U.S. Pat. Appl. No. 2010/0249345 teaches the formation of a catalyst “mud” or “paste” comprising a support bearing functional groups, a transition metal organometallic compound and specific activator compounds in an oil. Kaydol mineral oil and grease were used in the examples to form the catalyst paste.
U.S. Pat. Appl. No. 2003/0203809 relates to a catalyst composition comprising an activator, a support, a catalyst compound and an ionizing activator and which is formed in a diluent having a flash point of greater than 200° F. A suitable diluent is Kaydol mineral oil. The catalysts can be fed directly to a polymerization reactor as a slurry in mineral oil.
In U.S. Pat. No. 7,232,868 a polymerization process involves providing a catalyst slurry containing a metallocene catalyst and a first oil, providing a transport medium which is a second oil (which can be the same or different than the first oil), and combining the transport medium and the catalyst slurry to form a catalyst mixture which is then introduced into a polymerization reactor to polymerize olefins. The patent focuses on the mixing vessels and methods used to form the metallocene catalyst slurry and to combine the same with the transport medium. Propylene polymerization is preferred.
U.S. Pat. No. 7,645,843 describes a method for feeding a solid catalyst component to a polymerization reactor which involves suspending the solid component in an oil having a viscosity of 20 to 1500 mPa·s and subsequently metering the suspension into the reactor with a “valveless” piston pump. Preferably, the suspension further comprises a drag reduction reagent. Ziegler-Natta catalysts, chromium catalysts and supported metallocene catalysts are contemplated for use.
European Pat. No. 798,315 B1 discloses a method of making homogeneous mixtures comprising a metallocene catalyst in a viscous liquid hydrocarbon. The metallocene catalyst may be supported on an appropriate inert material. An exemplified liquid hydrocarbon is white mineral oil.
U.S. Pat. No. 7,005,398 discloses an olefin polymerization catalyst comprising a supported ionic activator, a metallocene compound, an organometallic compound and a “hydrocarbon” where the hydrocarbon can be a liquid hydrocarbon with a kinematic viscosity of 5.0 mm2/s or greater at 30° C., a solid hydrocarbon which is not a crystalline olefin polymer, or a crystalline olefin polymer. As an example of a crystalline olefin polymer, a polyolefin wax is taught. The catalyst is claimed to have improved storage shelf life.
In U.S. Pat. Appl. No. 2011/0130531 a spray dried solid polymerization catalyst comprising a supported metallocene catalyst is diluted in a liquid hydrocarbon to give a catalyst slurry. Injection of the catalyst slurry into a fluidized bed polymerization reactor gave a catalyst productivity of at least 12,000 grams of polyethylene per gram of the catalyst system. Mixtures of mineral oil and aliphatic hydrocarbons are used as diluents for the catalyst slurry formation.
Although mineral oil is often used to form catalyst slurries due to its relatively high viscosity, solid catalyst components have also been fed to a gas phase fluidized bed reactor as a slurry in a non-viscous hydrocarbon. U.S. Pat. No. 5,922,818 describes a method in which a measured amount of solid catalyst can be metered into a gas-phase reactor by first mixing it with a liquid hydrocarbon in a mixing chamber to form a suspension, followed by introduction into a gas-phase reaction zone. Solid metallocene catalysts are contemplated for use.
Slurry feed allows for catalyst modifier components to be sprayed into a reactor simultaneously with the polymerization catalysts. U.S. Pat. No. 6,245,868
provides a method of delivering a supported “bulky ligand metallocene” catalyst system to a gas phase polymerization reactor by utilizing a carrier solution comprising an antistatic agent and a liquid diluent, where the carrier solution serves to flush the supported catalyst system into the reactor. The method is said to improve catalyst delivery, catalyst efficiency and particle morphology. The method also avoids problems associated with dry catalyst feed such as catalyst injection tube plugging. The liquid hydrocarbon used is any capable of maintaining the antistatic agent in a dissolved state and includes numerous organic solvents such as volatile hydrocarbons selected from n-pentane, isopentane, n-butane, isobutane, n-hexane, etc. The use of mineral oil as a liquid diluent is not contemplated.
U.S. Pat. No. 6,720,396 describes the use of a supported catalyst composition in a slurry of hydrocarbon liquid, where the volume of the liquid is less than four times the pore volume of the support, and where the slurry is left to stand for a period of time before its use in a polymerization reactor. Slurry polymerization is preferred and the liquids contemplated for use do not include mineral oil.
Slurry feeding also allows for in-line mixing of various catalyst components which make up a final polymerization catalyst system. See for example, U.S. Pat. Appl. No. 2002/0107342, which describes a method for combining a catalyst component in a mineral oil slurry with a catalyst component in a liquid hydrocarbon on route to a fluidized bed reactor. The use of two different catalyst component carrier streams allows for quick modification of the catalyst component ratios before the catalyst enters the reactor. Both supported and unsupported catalyst components can be employed.
The use of small amounts of an inert hydrocarbon in combination with a supported catalyst is known to modulate polymerization kinetics. U.S. Pat. Nos. 7,705,095 and 7,528,090 teach the addition of an inert hydrocarbon to a supported constrained geometry catalyst in amounts which do not exceed the pore volume of the support. Such a catalyst, which remains a free flowing solid, nevertheless has a lengthened induction period when used in gas phase polymerization. The inert hydrocarbons contemplated by the ‘090’ patent included waxes, hydrocarbon liquids and oils. The inert hydrocarbons contemplated by the ‘095’ patent included lower alkanes or aromatics, with hexane being preferred. These patents also make reference to, but do not exemplify, the use of other supported catalyst systems such as chromium catalysts, Ziegler-Natta catalysts, metallocene catalysts and phosphinimine catalysts. The patents do not, however, teach the use of phosphinimine catalysts which are specifically substituted for enhanced gas phase polymerization activity and performance.
WO 96/34020 contains a similar teaching. Exemplified are supported metallocene catalysts coated with an inert material such as an inert hydrocarbon having a molecular weight of from 200 to about 5000, low molecular weight ethylene or styrene polyolefins and the like. Multiwax 195M and polyparamethylstyrene are used in the examples. The solid, supported catalysts coated with wax or polymer remained free flowing and reduced the tendency toward sheeting or fouling in a gas phase polymerization process.
European Pat. Appl. No. 924,226 A1 discloses a polymerization catalyst comprising a metallocene catalyst, a support material, an activator and a hydrocarbon or organic silicon material having a molecular weight of preferably more than 300. Liquid paraffins and waxes for example, were used as the hydrocarbon component.
U.S. Pat. No. 5,965,677 teaches the use of a supported phosphinimine catalyst. In the examples section, the patent specifically teaches that the supported catalysts may be coated with a thin layer of mineral oil in order to improve their shelf life stability before use. A suspension of a supported phosphinimine catalyst is fed to a gas reactor under positive nitrogen pressure. Although a wide variety of substituted and unsubstituted phosphinimine catalysts having the formula Cp(PI)MX2 (where Cp is a cyclopentadienyl type ligand, PI is a phosphinimine type ligand and each X is an activatable ligand) are considered, polymerization activity data was reported only for (C5H5)Ti(N═P(t-Bu)3)2X2 type catalysts which have an unsubstituted cyclopentadienyl ligand.
In a disclosure made at the 2002 Canadian Society for Chemistry Conference (“Cyclopentadienyl Phosphinimine Titanium Catalysts—Structure, Activity and Product Relationships in Heterogeneous Olefin Polymerization.” R. P. Spence; I. Mckay; C. Carter; L. Koch; D. Jeremic; J. Muir; A. Kazakov. NOVA Chemicals Corporation, CIC, 2002), it was shown that the addition of a fluorinated aryl group (e.g. C6F5), to a cyclopentadienyl ligand or an indenyl ligand of a supported phosphinimine catalyst can increase catalyst activity in a gas phase polymerization process. Disclosure of similar catalyst systems occurs in U.S. Pat. Appl. No. 2008/0045406 A1, which features a supported phosphinimine catalyst comprising a C6F5 substituted cyclopentadienyl ligand, and in U.S. Pat. Nos. 7,531,602, 7,064,096, 7,323,523 and 7,321,015, which discuss the use of supported phosphinimine catalysts having a 1,2-(n-propyl)(C6F5)Cp ligand, a 1,2-(n-butyl)(C6F5)Cp ligand and a 1,2-(n-hexyl)(C6F5)Cp ligand, mainly in dual catalyst formulations. The use of such catalysts, which have high activity in gas phase polymerization reactions, can lead to reactor operability issues including reactor fouling. None of the forgoing disclosures discuss the improvement to initiation kinetics possible when feeding similarly substituted, highly active, supported phosphinimine catalysts to a gas phase reactor as a slurry in a liquid hydrocarbon carrier such as, for example, mineral oil.